Illumination lenses act to collect light from a source and gather it into a useful beam to cast upon a target. Frequently, uniform illumination is desired, but most often not attained. Sometimes this is because the target, such as a room's floor, has widely varying distance and slant to the luminaire, so that uniform intensity becomes nonuniform illumination. In most cases, though, the luminaire itself has widely varying distance from its light source to its different light-redirecting sections. Thus both mirrors and lenses typically have nonuniform illumination across their exit apertures. The present invention addresses this problem with a general method of making a lens achieve uniform exit-aperture irradiance as well as uniform target irradiance. This capability is particularly important for the next generation of high-brightness light-emitting diodes (LEDs). Their comparatively high cost per lumen puts a premium on luminaire uniformity and efficiency, for which the present invention provides a significant boost.
A particular illumination field for such a device is downlights, ubiquitously seen in ceilings as comprising an incandescent spotlight bulb in a recessed can. These 50-100 W lamps must typically be replaced at least once per year. An LED downlight would be of great benefit, due to the much lower power consumption and ten times longer life of LEDs. Also, the low voltage of LEDs would enable LED downlights to be installed without the extremely high price of licensed electricians who must be used to install the otherwise low-priced conventional downlight cans.
Conventional LED optics, however, provide neither uniform output nor the high directionality required for a downlight to produce, for example, a small spot of light on a table. A standard target, moreover, is not round but a three-foot square that is nine feet distant from the lamp. Currently only expensive and bulky projection lamps can produce a square light beam, and quite inefficiently at that, by using large lenses to form an image of a square aperture placed in the output beam of a collimating lens or mirror that uses an incandescent lamp.
The present invention remedies the current lack of suitable optics for LED downlights, and in particular provides an LED downlight with a square spot.